Background-Cardiac resynchronization therapy (CRT) is widely applied in patients with heart failure and dyssynchronous contraction (DHF), but the electrophysiological consequences of CRT in heart failure remain largely unexplored. Methods and Results-Adult dogs underwent left bundle-branch ablation and either right atrial pacing (190 to 200 bpm) for 6 weeks (DHF) or 3 weeks of right atrial pacing followed by 3 weeks of resynchronization by biventricular pacing at the same pacing rate (CRT). Isolated left ventricular anterior and lateral myocytes from nonfailing (control), DHF, and CRT dogs were studied with the whole-cell patch clamp. Quantitative polymerase chain reaction and Western blots were performed to measure steady state mRNA and protein levels. DHF significantly reduced the inward rectifier K ϩ current (I K1 ), delayed rectifier K ϩ current (I K ), and transient outward K ϩ current (I to ) in both anterior and lateral cells. CRT partially restored the DHF-induced reduction of I K1 and I K but not I to , consistent with trends in the changes in steady state K ϩ channel mRNA and protein levels. DHF reduced the peak inward Ca 2ϩ current (I Ca ) density and slowed I Ca decay in lateral compared with anterior cells, whereas CRT restored peak I Ca amplitude but did not hasten decay in lateral cells. Calcium transient amplitudes were depressed and the decay was slowed in DHF, especially in lateral myocytes. CRT hastened the decay in both regions and increased the calcium transient amplitude in lateral but not anterior cells. No difference was found in Ca V 1.2 (␣1C) mRNA or protein expression, but reduced Ca V ␤2 mRNA was found in DHF cells. DHF reduced phospholamban, ryanodine receptor, and sarcoplasmic reticulum Ca 2ϩ ATPase and increased Na ϩ -Ca 2ϩ exchanger mRNA and protein. CRT did not restore the DHF-induced molecular remodeling, except for sarcoplasmic reticulum Ca 2ϩ ATPase. Action potential durations were significantly prolonged in DHF, especially in lateral cells, and CRT abbreviated action potential duration in lateral but not anterior cells. Early afterdepolarizations were more frequent in DHF than in control cells and were reduced with CRT. Conclusions-CRT partially restores DHF-induced ion channel remodeling and abnormal Ca 2ϩ homeostasis and attenuates the regional heterogeneity of action potential duration. The electrophysiological changes induced by CRT may suppress ventricular arrhythmias, contribute to the survival benefit of this therapy, and improve the mechanical performance of the heart.

Abstract-Atrial fibrillation is associated with increased expression of ventricular myosin isoforms in atrial myocardium, regarded as part of a dedifferentiation process. Whether reexpression of ventricular isoforms in atrial fibrillation is restricted to transcripts encoding for contractile proteins is unknown. Therefore, this study compares atrial mRNA expression in patients with permanent atrial fibrillation to atrial mRNA expression in patients with sinus rhythm and to ventricular gene expression using Affymetrix U133 arrays. In atrial myocardium, we identified 1434 genes deregulated in atrial fibrillation, the majority of which, including key elements of calcium-dependent signaling pathways, displayed downregulation. Functional classification based on Gene Ontology provided the specific gene sets of the interdependent processes of structural, contractile, and electrophysiological remodeling. In addition, we demonstrate for the first time a prominent upregulation of transcripts involved in metabolic activities, suggesting an adaptive response to increased metabolic demand in fibrillating atrial myocardium. Ventricular-predominant genes were 5 times more likely to be upregulated in atrial fibrillation (174 genes upregulated, 35 genes downregulated), whereas atrial-specific transcripts were predominantly downregulated (56 genes upregulated, 564 genes downregulated). Overall, in fibrillating atrial myocardium, functional classes of genes characteristic of ventricular myocardium were found to be upregulated (eg, metabolic processes), whereas functional classes predominantly expressed in atrial myocardium were downregulated (eg, signal transduction and cell communication). Therefore, dedifferentiation with adoption of a ventricular-like signature is a general feature of the fibrillating atrium. Key Words: atrial fibrillation Ⅲ gene expression Ⅲ atrial myocardium Ⅲ functional genomics A trial fibrillation (AF), the most common sustained arrhythmia, is associated with extensive structural, contractile, and electrophysiological remodeling, 1 stabilizing AF in the long run. Because current pharmacological treatment of AF is limited by ventricular proarrhythmia and inefficacy to prevent recurrences of AF, understanding the molecular events of these remodeling processes is essential for the development of new targeted therapeutic interventions. Even though knowledge of genes involved in remodeling processes exists on a gene-by-gene basis including transcripts of the extracellular matrix compartment, 2 ion channels, 1,3 and signal transduction molecules, 4 microarray analysis offers a broader and unbiased approach to identify pathophysiologically relevant pathways. Therefore, we performed a systematic functional analysis of gene expression in permanent atrial fibrillation (pmAF) based on information from the Gene Ontology (GO) database to relate expression changes of single transcripts to known remodeling processes.Moreover, atrial fibrillation has been shown to be associated with an atrial-to-ventricular switch by expr...

For the first time, independent microarray datasets pointed to significant involvement of immune response processes in end-stage DCM. Moreover, based on 4 independent microarray datasets, we present a robust gene expression signature of DCM, encouraging future prospective studies for the implementation of disease biomarkers in the management of patients with heart failure.

Objectives We examined the sodium-iodide symporter (NIS) which promotes in vivo cellular uptake of 99mTc or 124I, as a reporter gene for cell tracking by SPECT or PET imaging. Background Stem cells offer the promise of cardiac repair. Stem cell labeling is a prerequisite to tracking cell fate in vivo. Methods The human NIS cDNA was transduced into rat cardiac-derived stem cells (rCDCs) using lentiviral vectors. Rats were injected intra-myocardially with up to 4 million NIS+-rCDCs immediately following LAD ligation. Dual isotope SPECT (or PET) imaging was performed, using 99mTc (or 124I) for cell detection and 201Tl (or 13NH3) for myocardial delineation. In a subset of animals, high resolution ex vivo SPECT scans of explanted hearts were obtained to confirm that in vivo signals were derived from the cell injection site. Results NIS expression in rCDCs did not affect cell viability and proliferation. NIS activity was verified in isolated transduced cells by measuring 99mTc uptake. NIS+ rCDCs were visualized in vivo as regions of 99mTc or 124I uptake within a perfusion deficit in the SPECT and PET images, respectively. Cells could be visualized by SPECT up to day 6 post-injection. Ex vivo SPECT confirmed that in vivo 99mTc signals were localized to the cell injection sites. Conclusion Ectopic NIS expression allows non invasive in vivo stem cell tracking in the myocardium, using either SPECT or PET. The general approach shows significant promise in tracking the fate of transplanted cells participating in cardiac regeneration, given its ability to observe living cells using clinically-applicable imaging modalities.